feat(rust): allow to move G1 and G2 elements between threads (#87)

* feat: thread-safe elements

* chore: update recent code from develop

* chore: remove arc

* chore: implement Sync for elements

* fix: conflicting implementation

rust-bindings/bls-signatures/src/elements.rs

@@ -23,6 +23,10 @@ pub struct G1Element {
     pub(crate) c_element: *mut c_void,
 }
 
+// G1Element is immutable and thread safe
+unsafe impl Send for G1Element {}
+unsafe impl Sync for G1Element {}
+
 impl PartialEq for G1Element {
     fn eq(&self, other: &Self) -> bool {
         unsafe { G1ElementIsEqual(self.c_element, other.c_element) }
@@ -194,6 +198,10 @@ pub struct G2Element {
     pub(crate) c_element: *mut c_void,
 }
 
+// G2Element is immutable and thread safe
+unsafe impl Send for G2Element {}
+unsafe impl Sync for G2Element {}
+
 impl PartialEq for G2Element {
     fn eq(&self, other: &Self) -> bool {
         unsafe { G2ElementIsEqual(self.c_element, other.c_element) }
@@ -327,6 +335,7 @@ impl Drop for G2Element {
 
 #[cfg(test)]
 mod tests {
+    use std::thread;
     use super::*;
     use crate::{
         schemes::{AugSchemeMPL, Scheme},
@@ -381,4 +390,22 @@ mod tests {
 
         assert_eq!(g1_element.fingerprint(), 2093959050);
     }
+
+    #[test]
+    fn should_be_thread_safe() {
+        let bytes = [
+            151, 241, 211, 167, 49, 151, 215, 148, 38, 149, 99, 140, 79, 169, 172, 15, 195, 104,
+            140, 79, 151, 116, 185, 5, 161, 78, 58, 63, 23, 27, 172, 88, 108, 85, 232, 63, 249,
+            122, 26, 239, 251, 58, 240, 10, 219, 34, 198, 187,
+        ];
+
+        let g1_element =
+            G1Element::from_bytes(&bytes).expect("should create g1 element from bytes");
+
+        let test_thread = thread::spawn(move|| {
+            assert_eq!(g1_element.fingerprint(), 2093959050);
+        });
+
+        test_thread.join().unwrap();
+    }
 }